War machines in Heroes V.

Everything is clear with the ballista (or rather, nothing is clear), but could you tell me how a first aid tent can restore (revive) a unit? You can apply a bandage during first aid, but I don't know how it can revive. In our hospitals, resuscitation is powerless, but here there's some kind of magical first aid tent. I'm for it restoring health, like in Heroes of Might and Magic III, instead of reviving.